CN108475575B

CN108475575B - Electronic device comprising at least one inductor comprising a passive thermal management device

Info

Publication number: CN108475575B
Application number: CN201680074602.9A
Authority: CN
Inventors: 杰拉德·蒂列特; 皮埃尔·皮尔维斯
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2015-12-17
Filing date: 2016-12-16
Publication date: 2020-08-28
Anticipated expiration: 2036-12-16
Also published as: EP3391394A1; US20190392975A1; JP2019503073A; KR20180096700A; WO2017103078A1; US10629353B2; EP3391394B1; CN108475575A; RS60989B1; FR3045922A1; JP6895969B2; FR3045922B1

Abstract

An electronic device comprising a carrier (2), at least one active element (4) and at least one inductor (6), the inductor (6) comprising a core (10) and a winding (12) around at least a part of the core, the core (10) defining at least a part of a magnetic circuit along which magnetic flux lines are intended to travel. The core (10) comprises a body (14) comprising at least two portions defining two successive regions of the magnetic circuit, each portion having a thickness that is small with respect to its length and width, each portion comprising a surface that is lateral with respect to the direction of the magnetic circuit, one portion being in direct contact with the carrier by a portion of its lateral surface, the other portion being positioned with respect to the carrier (2) so that its lateral surface is not in contact with the carrier (2).

Description

Electronic device comprising at least one inductor comprising a passive thermal management device

Technical Field

The present invention relates to an electronic device comprising at least one magnetic inductor comprising a passive thermal management means, such as a power converter.

Background

In the field of power electronics, inductors comprising a ferromagnetic core at least partially surrounded by an electrically conductive winding are mainly used as passive elements for power converters. The power converter may operate at a frequency between 100kHz and 10MHz and may deliver 0.1kW to 100kW of power. These converters are used in particular in the field of energy production to supply electric motors and electronic systems (electronic devices, portable computers). In these fields of application, the inductance value of the converter is between 1 μ H and 10 mH.

An inductor comprises a core and an electrical conductor, called a winding, which is arranged in N turns around a portion of the core. The core includes a ferromagnetic material. During operation, an alternating current is passed through the windings, thereby generating magnetic induction in the core having the same frequency. Losses occur as magnetic induction is generated, which leads to an increase in the temperature within the magnet core. These damages increase with the operating frequency of the inductor, requiring thermal management above about 1MHz to cool the core and prevent unacceptable temperature increases.

A power converter is an electronic device that has the function of varying the voltage and current output by a power source to supply power to a distribution grid or a given electrical system according to specifications. The converter comprises electronic elements, called active elements, which operate like switches, switching at a given frequency. In the case of a DC/DC converter, for example, the active element is a transistor for "chopping" the input voltage at regular periods. To output the dc output voltage, the inductor is also used to store and recover power during each cycle and to smooth the output voltage to its average value. These so-called "passive" elements are used for the operation of the converter, but they may occupy up to 40% of the volume and cost of the converter.

The operating frequency of the converter is typically in the range of 10kHz-500 kHz. Due to GaN technology, transistors can be manufactured that can switch at very high frequencies (e.g. frequencies greater than 1 MHz), so that converters can be manufactured that operate at higher frequencies.

First of all, an increase in the operating frequency should be of particular interest, since the volume of the passive components of the converter can be reduced, thus reducing the size, mass and cost of these devices. By increasing the switching frequency, the number of electrical cycles is increased, thus increasing the ability to be delivered by the core in a given time by the same proportion. Since the power of the converter remains constant, the volume of the magnetic inductor can be reduced in inverse proportion to the frequency.

This reduction in the volume of the magnetic core is particularly useful for making smaller, lighter weight and less expensive transducers. Such converters are expected to be used in the aeronautical and automotive industries.

Secondly, an inductor compatible with a power converter operating at a frequency between 100kHz and 10MHz and a power between 0.1kW and 100kW is characterized by an inductance L having a value between 1 muH and 10mH and a volume greater than 1cm³. In the context of such a transducer, the best suited inductor is monolithic, unlike technologies based on thin film or multilayer LTCC structures, which are limited to powers of less than 10W.

Monolithic inductors are constructed from a single piece of ferromagnetic material that forms a core. The material is characterized in that the value of the relative magnetic permeability μ r is high, for example, more than 50, and the saturation magnetic induction Bs is, for example, more than 100 mT.

The ferrite type oxide material having a spinel crystal structure has a permeability value stable at high frequency. This is why they are very widely used as inductor cores, especially operating at high frequencies (100kHz < f <10 MHz). The most frequently used formulations are (Mn1-xZnxFe2O4) and (Ni1-xZnxFe2O 4). These materials are also characterized by high values of resistivity, which limits damage caused by induced currents.

Although they are optimal, these ferromagnetic materials are a source of energy dissipation processes also known as magnetic losses. These magnetic losses are dissipated in all respects as heat in the volume of the core. Therefore, although the volume of the core can be reduced by the increase of the frequency and 100W/cm can be realized³But it is necessary to limit the heat dissipation in the core to prevent the temperature of the core from rising excessively.

This is particularly the case because the magnetic losses increase with the frequency and the peak value of the magnetic induction.

Furthermore, it has been shown that a small inductor volume tends to generate more heat in the core. For example, a 1kW converter (200V/400V) functioning at 5MHz requires an inductance of 10 μ H. A compact 4F1 ferrite core (E-E) can be designed to make an inductor. For a value corresponding to 100W/cm³10cm of specific power³The calculated core internal temperature reached 210 c, taking into account the natural convection method of the heat rejected.The volume of the inductor needs to be increased to 50cm³To reduce the temperature to a value of 70 c that is acceptable for the material.

It has been proposed that heat can be reduced by improving the heat exchange at the surface of the core. For example, a temperature regulation system including a heat exchanger may be used, but this temperature regulation system makes the converter compact and smaller and increases the cost of the converter.

It is also known to reduce the effective permeability by creating air gaps in the core to reduce induction and to reduce heat in a good way. But increasing the air gap increases the size of the core and may reduce the electromagnetic compatibility of the inductor due to the magnetic field radiating in the air gap.

It has also been proposed that planar inductors can be manufactured in which the thickness of the core is small relative to the length and width of the core.

Document US 9001524 describes an integrated circuit comprising an inductor forming a frame, the core being flat and in the form of a frame surrounding a carrier. The inductor also takes up a large space on the carrier and the heat exchange is not optimal.

Disclosure of Invention

It is therefore an object of the present invention to provide a very compact electronic device comprising at least one active element and at least one inductor, and having good thermal management.

The above object is achieved with a device comprising a carrier, at least one active component fixed on the carrier and at least one inductor, the inductor comprising a magnetic core and a conductor partially surrounding the core, the core comprising a body having a very small ratio of thickness to length. The body at least partially defines the magnetic circuit, the body comprising at least one first portion and one second portion defining two successive regions of the magnetic circuit, the first portion being in contact with the carrier, the second portion being located in a suitable position with respect to the carrier so as to have a small contact with the carrier.

For the purposes of the present application, the term "magnetic circuit" means a path followed by magnetic flux lines generated in a core by an electric current circulating in an electric conductor surrounding a portion of the core. The magnetic circuit follows the closed magnetic circuit. The magnetic circuit may comprise a plurality of portions of different materials, such as a core and an air gap; each section has its own section and length.

Thus, the surface of the second portion for which the contact with the carrier is reduced may exchange heat and cool the core more efficiently. Thus, thermal management of the core is facilitated. Furthermore, the arrangement of the second portion enables to free space for other components fixed on the carrier and/or to reduce the area of the carrier. A portion of the core occupies an area above the carrier, typically defined by the package, and typically unoccupied. Thus, the device can be made more compact while limiting the temperature rise of the core.

Very advantageously, the second portion of the core is in large-area thermal contact with an element, such as a plate, which is even more efficient in exchanging heat by convection. Thermal management of the inductor is further improved. The package itself may help to remove heat from the core.

In other words, a device is manufactured in which the inductor comprises a magnetic core in the form of a strip shaped and/or arranged to form a three-dimensional structure, a portion of which is not in contact with the carrier to increase the heat exchange area, which enables to occupy the unoccupied area of the device, to make the device more compact and to limit the core heating.

In one example embodiment, the ferromagnetic core includes thin flat portions to reduce the volume of the core, improve heat exchange, and reduce the volume occupied by the inductor in the converter. The flat portions forming the core are fitted or joined together to form a long three-dimensional structure having a small cross-section forming the magnetic circuit. The three-dimensional structure is designed such that it occupies the smallest possible volume in the converter, in particular with the available volume.

One subject of the invention is thus an electronic device comprising a carrier, at least one active element and at least one inductor, said inductor comprising a core and an electrical conductor surrounding at least part of the core, the core delimiting at least part of a magnetic circuit along which magnetic flux lines are intended to travel, the core comprising a body having at least two portions defining two successive areas of the magnetic circuit, each portion remaining thinned with respect to its length and width, each portion comprising a lateral surface with respect to the direction of the magnetic circuit, one portion being in direct contact with the carrier by means of a portion of its lateral surface, the other portion being positioned with respect to the carrier so that its lateral surface is not in contact with the carrier.

Advantageously, the ratio between thickness and length is between 1/200 and 1/10, and the ratio between thickness and width is between 1/20 and 1.

In one example embodiment, the core may include an air gap between the first portion and the second portion.

The electronic device may comprise a package mounted on a carrier, the package and the carrier defining a volume in which the at least one active element and the inductor are accommodated.

Preferably, at least a second portion of the inductor is shaped to fit into said volume.

In an example embodiment, the second portion is integrated in a wall of the package.

In a very advantageous example, the apparatus may comprise at least one heat exchanger plate thermally connected to the core. For example, the apparatus may comprise at least one thermally conductive and electrically insulating element in contact with the core and the heat exchanger plate. The heat exchanger plate may form at least a part of a wall of the package.

In an example embodiment, the electrical conductor forms a winding, the winding comprising a portion integrated in the carrier.

Preferably, the carrier is an integrated circuit.

Another subject of the invention is a converter comprising at least one electronic device according to the invention, the active element being a transistor.

Another subject of the invention is a method of manufacturing an electronic device according to the invention, the method comprising the steps of:

a) providing a carrier, and making the carrier into a shape,

b) providing an active element and mounting the active element on a carrier,

c) the manufacture of the inductor core is carried out,

d) the core is assembled on a carrier and,

e) windings are provided and assembled.

During step c), the strip intended to form the first and second portions can be manufactured, for example, by casting a strip of paste containing a powder of ferromagnetic material or by injection moulding of a powder from a raw material comprising a strip of ferromagnetic material.

During step c), the strip may be manufactured into a desired shape.

During step c), for example, at least a portion of the tapes are fixed to each other to make a portion of the core.

During step d), the tape may be assembled to form a core.

In an advantageous embodiment, one part of the winding is manufactured before the core is assembled and the other part is manufactured after the core is assembled.

Drawings

The invention will be better understood after reading the following description and the accompanying drawings, in which:

fig. 1 is a perspective view of an exemplary embodiment of an electronic device according to the present invention.

Fig. 2 is a top view of a detail of the manufacture of an electronic device according to another example embodiment.

Figure 3 is a side view of figure 2.

Detailed Description

Fig. 1 shows an example of an electronic inductor device, such as a power converter, according to the present invention.

The device in fig. 1 comprises a carrier 2 consisting of a thin rectangular plate, at least one active element 4, such as a transistor, fixed to the carrier 2, at least one inductor 6 and a package 8. The carrier 2 extends in a plane O1. The size of the carrier in plane O1 is indicated by d1 and d 2. The carrier may for example be an integrated circuit, in which the at least one active element 4 may be formed integrated.

Inductor 6 includes a magnetic core 10 and an electrical conductor 12 or winding surrounding at least a portion of core 10.

When current flows in the winding 12, magnetic flux lines flow in the core along the magnetic circuit. In the case of a core in the form of a rectangular frame, the flux lines form a closed loop. The magnetic flux lines travel along the magnetic circuit, which extends along the entire length of the core.

The magnetic core 10 includes a body 14, the body 14 being formed from a continuous strip or a series of strips. The body of the core may for example be made of spinel ferrite such as NiZn and MnZn such as NiZn 4F 1.

Each strip has a thickness e, a width L and a length L. The product e × L corresponds to a section of the core which is also equal to the magnetic section a of the core.

The thickness e is much smaller than the width L and the length L, preferably by a factor of at least 10.

These proportions of the dimensions of the strip facilitate the integration of the core, since the strip thus formed may be shaped, for example curved or convex, to match a non-planar surface, which is not possible with thicker strips.

For example, e is between 1mm and 5mm, L is between 5mm and 20mm, L is between 50mm and 200mm, and e/L-1/10 and e/L-1/100.

It is contemplated that the dimensions (i.e., thickness and/or width) of the core vary along the length of the magnetic circuit.

The belt comprises side surfaces comprising, in the case of a belt having a rectangular parallelepiped shape, two rectangular surfaces having a large area equal to L × L and two smaller rectangular surfaces having a smaller area equal to e × L.

In the example shown in fig. 1, the body 14 of the core comprises eight straight sections, indicated as P1, P2, P3, P4, P5, P6, P7, P8. The eight portions define a loop within which the lines of magnetic flux circulate. In the example shown, the eight portions are straight and extend along a longitudinal axis, each portion comprising two longitudinal ends.

In the example shown, the portions P1 and P5 are in contact with the carrier 2 through a portion of their side surfaces. In the example shown, the portions P1 and P5 are in contact with the carrier by one of their larger area surfaces.

As a variant, the portions P1 and P5 of the core that are in contact with the carrier can rest on the carrier by means of one of the surfaces of smaller area.

The parts P1 and P2 firstly fix the inductor on the carrier and secondly form an electrical connection with other elements of the device. In the example shown, the arrangement of the portion P5 also enables the windings to be integrated in the carrier. The winding 12 is arranged around a part of the portion P5, and the manufacture of the winding 12 will be described below. This integrated embodiment reduces the size of the inductor even further. It will be understood, however, that an inductor in which the windings are constituted by a continuous wire, in particular around at least one of the portions P2 to P4 and P6 to P8, is not outside the scope of the present invention.

The portions P1 and P5 are arranged parallel to each other and extend over the entire dimension d1 of the carrier.

The sections P2, P3, P4 are arranged relative to each other to form an inverted U, with P3 forming the bottom of the U and sections P2 and P4 forming the legs of the U. The U thus formed lies in a plane orthogonal to plane O1. The U is arranged relative to sections P1 and P5 such that the legs of the U are connected to sections P1 and P5. The configuration of the portions P6, P7 and P8 is similar to that of the portions P2, P3 and P4, the portions P6, P7 and P8 being arranged in a plane orthogonal to the plane O1 and parallel to the plane containing the portions P2, P3 and P4.

Preferably. An air gap is provided between two consecutive core portions. The manufacture of the inductor is simplified because the core can be made of planar parts. As a variant, it is possible to bring some parts into contact with each other, or even all parts, so as to form a closed core. Also as a variant, one or more air gaps may be provided in portion P1 and/or portion P5.

The lateral surfaces of the portions P2, P3, P4 and of the portions P6, P7, P8 are not in contact with the carrier and can exchange heat with the external environment by convection. The core can then have a very large heat exchange area, since it comprises the entire lateral surface of the portions P2, P3, P4, the entire lateral surface of the portions P6, P7, P8 and most of the lateral surfaces of the portions P1 and P5. It should be noted that a part of the side surfaces of the portions P1 and P5, which are in contact with the carrier, exchange heat with the carrier by conduction and participate in cooling the core.

Furthermore, the core occupies a portion of the volume above the carrier, which may free space on the carrier or reduce the surface area of the carrier. Advantageously, the core is shaped to fit the internal volume of the package, thus occupying a volume that is not normally used.

In a very advantageous embodiment, the walls of the package may be arranged to be shaped to receive a portion of the core. For example, the portions P2, P3, P4 and the portions P6, P7, P8 may be integrated in the thickness of the walls of the package, further reducing the space occupation of the core and benefiting the heat exchange with the outside.

The winding can be manufactured, for example, as follows: the complete winding is formed, for example, using microelectronics techniques by forming a first half winding in the substrate, forming a portion of the core over the first half winding, and forming a second half winding over the portion of the core. An example of such a method is described, for example, in document US 2009/0160595. Such an inductor occupies an even smaller volume.

It will be appreciated that the number and shape of the portions may vary. The number of portions of the side wall of which a portion is in contact with the carrier may also vary. For example, all or some portions may be flexible. It is possible to envisage manufacturing the monolithic core body directly in a three-dimensional shape.

Further, the relative arrangement of the portions with respect to each other may also vary. For example, the portion of the side wall thereof not in contact with the carrier may be inclined with respect to the plane of the carrier.

Preferably, the body is shaped so that its projection on the plane O1 is received within the projection of the carrier, so that the entire device can be integrated in a package covering the carrier.

In the example shown, the core is symmetrical about a plane orthogonal to the plane O1, but this is not a limiting case and any other shape capable of providing a long magnetic circuit, preferably occupying the space above the carrier, can be used.

In one advantageous example, portions of the core can be combined with heat exchange means to improve the removal of heat generated in the core.

Figures 2 and 3 show an example embodiment of a detail of a core using such a device.

This example includes a portion of the core in the form of a U made up of portions P2, P3, P4. The plates 15 are placed on each side of the U inside the space delimited by the U. The plate 15 is made of a material having very good thermal conductivity, such as AlN or copper having a low electrical conductivity property.

In the example shown, the outer dimensions of the plate and the inner dimensions of the U are such that there is no contact between the plate and the portions P1, P2, P3. A thermally conductive and electrically insulating element 16, for example made of AlN, is arranged to form thermal connections between the various parts and the plate. The gaps between the plate 15 and the sections can for example be used to form a winding around one leg.

The thermally conductive and electrically insulating element prevents magnetic flux from leaking into the vicinity of the core, thereby generating induced current.

Thus, heat generated in the core is transferred to the heat exchange plates by conduction through the elements 16, and then the heat is discharged by convection.

In case the heat exchanger plates are made of an electrically insulating material, a direct contact between the core and the heat exchanger plates may be established as shown in fig. 1, heat being directly discharged from the core to the heat exchanger plates.

In the example shown, the heat exchanger plates are located inside the space delimited by the portions of the core, so that the edges of the plates face the sides of the segments, but the plates are arranged so that one face of the plates faces or even is in direct contact with the portions of the core. As a variant, a single plate 15 may be used.

As shown in fig. 1, the heat exchanger plate may for example be integrated in the package, e.g. the heat exchanger plate may form part of a wall of the package. Thus, the heat exchange by convection is improved.

According to an advantageous example, it is also possible to bring one or more heat exchange plates in thermal contact with the portions P1 and P5 supported on the carrier, to increase the area of exchange with the outside, while improving the heat discharge from the core, due to the greater contact between the plates and the core. For example, one plate may contact a side of the portion opposite the side contacting the carrier. A window can be formed in the plate so that other elements can pass through. The plates may be contoured to increase heat exchange. As a variant, a plate may be placed on each side of the portions P1 and P5.

Very advantageously, fins can be provided on the side surfaces of the portions and/or on the package to further increase the heat exchange. Preferably, the fins are oriented such that the fins are substantially parallel to the lines of magnetic flux.

By comparison, a 1kW DC/DC voltage step-up converter (200/400V) required a storage inductance of 10 μ H to operate at 5 MHz. This inductance can be obtained by assembling two standard E-type ferromagnetic elements, known in the art, occupying 50cm³And has a total volume of 200cm²The exchange area of (a). There are other core shapes with smaller volumes, but other core shapes also have smaller heat exchange areas, and their use increases the operating temperature of the inductor.

Thanks to the invention, the same transducer can be formed with a core having 10cm³While maintaining a volume of 200cm²The exchange area of (a). For example, the core then comprises a strip whose thickness e is equal to 4mm and width L is equal to 9 mm. The total length l of the magnetic circuit required is 300 mm. The core may be made of side-by-side ten strips having the same length of 30mm and arranged to form the circuit of figure 1. The side and bottom surfaces may be developed to 200cm²Total exchange area of (a).

Now, a method of manufacturing the device according to the present invention will be described.

The manufacturing method comprises the following steps:

a) providing a carrier, and making the carrier into a shape,

b) providing an active element and mounting the active element on a carrier,

c) the manufacture of the inductor core is carried out,

d) the core is assembled on a carrier and,

e) windings are provided and assembled.

Step a) may comprise a carrier manufacturing step, such as a step of manufacturing an integrated circuit.

Step b) may occur simultaneously with step a), in particular when the carrier is an integrated circuit, and the active elements, such as transistors, may be fabricated simultaneously with the integrated circuit.

Step c) may comprise steps d) and e):

advantageously, the core portion can be manufactured by a belt molding process, which is particularly suitable for manufacturing thin parts, for example of the order of 1 mm.

A fabricated part is utilized that includes a ferromagnetic material powder dispersed in a solvent and an organic binder. This preparation is called a slurry. The slurry is spread on a planar carrier, for example, using a pad with a blade mounted thereon. The movement of the blade causes the slurry deposited on the blade to be sheared and smoothed, providing good planarity and uniform deposition. The thickness of the resulting tape can be controlled by adjusting the height of the blade. The thus formed tape is then subjected to various evaporation and drying treatments to eliminate some of the solvent. Such tape molding methods are known to those skilled in the art. At this stage, the belt is flexible and easy to handle. In particular, the tape can be easily cut into a specific pattern using a conventional cutting tool.

At this stage, it is also possible to fold or bend the strip on a carrier, which gives the strip a profile.

In the present invention, portions of the core may be formed in this manner. For example, a template of, for example, aluminum having the desired contour may be used. For example, the template may be manufactured by machining. The ribbon is deposited on a template and then bent by applying mechanical force to match it to the shape. The assembly is heat treated at high temperature to sinter the strip. Sintering is accompanied by shrinkage of the material in all directions by approximately 10% -15%, the cut size of the green tape and the size of the template allowing this shrinkage.

In a variant embodiment, the strip comprising ferromagnetic material may be assembled and welded to other strips made of different materials, the properties of which are determined to make some heat-conducting elements and windings. The assembly is then sintered together to produce all or some of the inductors.

According to another exemplary embodiment, the portions of the core of the inductor are manufactured by Powder Injection Molding (PIM).

The first step of the PIM process is to obtain raw materials suitable for the target application. The raw material consists of a mixture of organic material (or polymeric binder) and inorganic powder (metal or ceramic) that will form the final part. The feedstock is then injected into the injection press as a thermoplastic using techniques known to those skilled in the art. Molding melts the polymer injected into the cavity with the powder and imparts the desired shape to the mixture. During cooling, the mixture solidifies and includes the shape imparted by the mold.

After removal from the mold, a different thermal or chemical treatment is applied to the part to remove the organic phase. The elimination of the organic phase during this step (known as degreasing) leaves a space in the blank with a porosity of between 30% and 50%. Patent US 8940816B2 describes a process for preparing raw materials and degreasing in the case of production by PIM.

After degreasing, the porous blank contains only powders of inorganic material. The blank is then densified to form the final densified component. The porous blank is consolidated by high temperature sintering, for example at over 1000 c, in a furnace operating at an atmosphere suitable for the type of material used. When the optimum density is achieved, the part is cooled to ambient temperature.

During step c) it is possible to manufacture straight strips which are subsequently to be assembled with each other and/or arranged with respect to each other to form a three-dimensional core according to the invention or to manufacture a monolithic core comprising at least a portion for assembling the core on a carrier.

At this stage, the sintered band forms a rigid element that can be manipulated. These elements are particularly stable, can be exposed to mechanical stresses of, for example, several MPa, and temperature rises of, for example, the order of hundreds of degrees. The tape may be mounted, for example, by gluing, for example using a thermally conductive glue. For example, the strip may be fitted and inserted into a correspondingly shaped housing in the carrier and/or package.

These shells can be manufactured by moulding, for example, when the package and/or the carrier are made of plastic. The tape may be held in place by mechanical means, for example by crimping or by gluing, for example using epoxy.

Step e) may be accomplished using the techniques described in document US2009/0160595 above. In this case, steps d) and e) occur simultaneously.

The invention is particularly suitable for making compact power converters operating at high frequencies, since the inductor can limit core heating very efficiently.

Claims

1. Electronic device comprising a carrier (2), at least one active element (4) and at least one inductor (6), said inductor (6) comprising a magnetic core (10) and an electrical conductor (12) surrounding at least a portion of said magnetic core, said magnetic core (10) delimiting at least a portion of a magnetic circuit along which magnetic flux lines are to travel, wherein said magnetic core (10) is located at one side of said carrier (2) and comprises at least one first portion (P1, P5) and one second portion (P2, P4, P6, P8) defining two successive areas of said magnetic circuit, each of the first portion (P1, P5) and the second portion (P2, P4, P6, P8) having a strip shape with a small thickness with respect to its length and width, each of the first portion (P1, P5) and the second portion (P2, P4, P6, P8) comprising a lateral surface with respect to the direction of said magnetic circuit, the first portion (P1, P5) is in direct contact with the carrier by a portion of its side surface and is surrounded by the electrical conductor (12), the second portion (P2, P4, P6, P8) being positioned with respect to the carrier (2) such that its side surface is not in contact with the carrier (2), wherein, for each of the first portion (P1, P5) and the second portion (P2, P4, P6, P8), the ratio of thickness to length is between 1/200 and 1/10, the ratio of thickness to width is between 1/20 and 1.

2. The electronic device of claim 1, wherein, for each portion, a ratio of thickness to length and a ratio of thickness to width is at least less than 1/10.

3. The electronic device of claim 1 or 2, wherein the magnetic core (10) comprises an air gap between the first portion (P1, P5) and the second portion (P2, P4, P6, P8).

4. Electronic device according to claim 1 or 2, comprising a package (8) mounted on the carrier (2), the package (8) and the carrier (2) defining a volume in which the at least one active element (4) and the inductor (6) are accommodated.

5. The electronic device of claim 4, wherein the second portion (P2, P4, P6, P8) is integrated in a wall of the package (8).

6. The electronic device according to claim 1 or 2, comprising at least one heat exchanger plate (15) thermally connected to the magnetic core (10).

7. The electronic device according to claim 6, comprising at least one thermally conductive and electrically insulating element (16) in contact with the magnetic core (10) and the heat exchanger plate (15).

8. The electronic device according to claim 6, comprising a package (8) mounted on the carrier (2), the package (8) and the carrier (2) defining a volume in which the at least one active element (4) and the inductor (6) are accommodated, and wherein the heat exchange plate (15) at least partially forms a wall of the package (8).

9. The electronic device according to claim 1 or 2, wherein the electrical conductor (12) forms a winding comprising a portion integrated in the carrier (2).

10. The electronic device according to claim 1 or 2, wherein the carrier (2) is an integrated circuit.

11. Converter comprising at least one electronic device according to one of claims 1 to 10, wherein the active element is a transistor.

12. Method of manufacturing an electronic device according to one of claims 1 to 10, comprising the steps of:

a) providing a carrier, and making the carrier into a shape,

b) providing an active element and mounting said active element on said carrier,

c) the magnetic core is manufactured by the following steps,

d) -mounting said magnetic core on said carrier,

e) windings are provided and assembled.

13. Manufacturing method according to claim 12, wherein during step c), the strip intended to form the first and second portions is manufactured, advantageously by casting a strip of paste containing a powder of ferromagnetic material or by injection moulding of a powder from a raw material comprising a strip of ferromagnetic material.

14. Manufacturing method according to claim 13, wherein during step c) the strip is placed in a desired shape.

15. Manufacturing method according to claim 13 or 14, wherein during step c) at least a part of the strips are fixed to each other to manufacture a part of the magnetic core.

16. A manufacturing method according to claim 13 or 14, wherein during step d) the strip is assembled to form the magnetic core.

17. Manufacturing method according to one of claims 12 to 14, wherein one part of the winding is manufactured before the magnetic core is assembled and another part is manufactured after the magnetic core is assembled.